NL8303551A - LIGHTVISOR CONSISTING OF A LIQUID CRYSTAL DIRECTED BY AN ELECTRON BEAM AND METHOD OF MANUFACTURING THAT. - Google Patents

Description

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Title: Light valve consisting of an electron beam-directed liquid crystal and method for its manufacture.

The invention relates to display devices and their manufacture, in particular to light modulators based on an electron beam-directed liquid crystal.

There are many applications in which it is desirable to modulate light to form an image based on information from an electrical signal. Such applications include the projection of television images or computer-supplied data or drawings onto a screen.

Projection devices using the interaction light valve technology are generally divided into two groups: (1) those in which the light modulator is connected to the directing system via a photoconductor; and (2) those in which the light modulator is directed directly, usually using an electron beam or laser. An example of the former type is a liquid crystal light valve mentioned in J. Grindberg, et al., "Photoactivated Birefringent Liquid Crystal Light Valve for Color Symbology Display", IEEE Trans.Elec.Dev., Vol. ED-22, No. 9, p. 775 (1975) and W.

20 Bleha, et al., "Application of Liquid Crystal Light Valve to Real-Time Optical Data Processing," Opt.Eng., Vol. 17, no. 4, p. 371 (1978). In the above-mentioned device, a field is applied to a reflective liquid crystal cell by a photoconductor which is activated by light incident on one side, whereby the cell modulates light entering the other side and bouncing through it. However, this type of device uses a complex layered structure and complicated optics, and for a practical thickness of the liquid crystal cell, the switching speed and contrast ratio are insufficient for some suitable applications.

Examples of the second type of light modulator are oil film devices mentioned by T. True, "Recent Advances in High Brightness and High Resolution Color Light Valve Projector," 10 SID Symposium Digest, Vol. 10, p. 20 (1979); a deformagraphic mirror device described by Wohl et al., U.S. Patent 3,626,084 issued December 7, 1971, entitled: Deformographic Storage Display Tube; "a thermally oriented smectic liquid crystal light valve described by 5 H. Dewey, et. al., "Laser-Addressed Liquid Crystal Projection Displays," SID Proceedings, Vol. 19, No. 1, p. 1 (1978) and M. Smith, et al., "Ultra High Resolution Graphic Data Terminal," SPIE, Vol. 200, 171 (1979); a mirror matrix device described by R. Thomas, et al., "The Mirror 10 Matrix Tube: A. Novel Light Valve for Projection Displays," Westinghouse Scientific Paper, 74-Ig7- Mirro-Pl (ES 481), November 1974, by G. Guldberg, et al., "An Aluminum / SiO2 / Silicon on Saphire Light Valve Matrix for Projection Displays," Applied Physics Letters, Vol. 26, No. 7, p. 391 (1975), and 15 by L. Hornbeck, et al., "Deformable Mirror Projection Display" 11 SID Digest, Vol. 11, p. 229 (1980); and a device at b asis of the pockels effect, mentioned by G. Marie and J. Donjon, "Single Crystal Perroelectrics and Their Application in Light Valve Display Devices," Proc. of the IEEE, Vol. 6, 20 No. 7 (1973).

The above mentioned devices in the second group have several drawbacks. The oil film, deformigraphic mirror, thermally oriented, and matrix mirror devices all require Schlieren optics, which are complicated and optically ineffective. Moreover, like the pockel effect device, they are all reflective devices.

The oil film-based devices, where an image is written by an electron beam onto a thin oil film, require very good maintenance and complicated tool construction due to the breakdown of the oil film as well as a cathode through the electron beam. The deformagrammatic, thermally oriented and matrix mirror devices are all storage devices that use modulation media with a limited switching speed that limit their use in other applications. The deformigraphic device, which uses a flexible membrane to modulate the light, does not have a low-frequency spatial representation and causes bending of the membrane. The thermally oriented device has a low sensitivity. The device based on the Pockels-8303551-3 effect, in which light is modulated by a KDP (potassium dihydrophosphate) crystal, which is written by an electron beam, is a complex device that requires a cooling system and the resolution of which is limited by the small size of a practical crystal.

Liquid crystal materials are attractive to image projection devices because of their selectively controllable light modulation properties. One limitation of their application so far, however, is the lack of a satisfactory directional scheme. It is desirable to direct a liquid crystal cell directly with an electron beam because the cathode ray tube (hereinafter referred to as "CRT") technology is highly developed. A reflective type liquid crystal CRT television device is n.1. described by J. VanRaalte, Proc. of the 15 IEEE, vol. 56, no. 12, p. 2146 (1968). However, in that case, the electron beam was coupled to the liquid crystal cell by a number of metal pins, leading to a number of problems, such as low resolution and a pin-to-pin cross connection. Electron beam scanning of a liquid crystal material for storing information has also been described by J. Hansen and R. Schneeberg "Liquid Crystal Media for Electron Beam Recording," IEEE Trans.on Elec.Dev.,

Full. ED-15, No. 11, p. 896 (1968), although the device described therein uses a cholesteric liquid crystal, the display time of which is slow and necessitates switching a high electric field, leading to low sensitivity. In addition, the possible use of a liquid crystal cell in an electron beam direct image storage device has been described by I. Chang 30 and W. Pennebaker, "Bi-stable Storage Tube with AC Controlled Display," 1973 SID Symposium Digest of Technical Papers, p.

102.

However, none of the aforementioned publications provide a fast display device that teaches light modulation passing through the device for satisfactory projection, without the use of complex optical instruments, with rapidly changing images, such as those be formed by a television. Therefore, there was a need to develop such a device.

8303551 * -4-

The present invention addresses the above-mentioned need and overcomes the above-mentioned drawbacks of the prior art image projection devices by providing a liquid crystal light valve which modulates light when it is transmitted through the light valve and can be directly directed by a scanning electron beam, such as in a cathode ray tube. The light valve according to the invention can be used with a simple optical transmission system to project rapidly changing images, it has high resolution, contrast and sensitivity, and it is believed to provide greater reliability than the known devices. The invention also provides a method of assembling a projection system using a cathode ray tube with windows through which light passes to be modulated, which is then projected onto a screen. The invention therefore provides a new method for assembling such a light valve.

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A switched nematic liquid crystal cell 20 is formed using a suitable liquid crystal material sandwiched between a transparent face plate having a transparent electrode formed thereon and a transparent target, the central portion of the cell defining a window through which light can be transmitted for modulation. .

A writing electron gun is provided to direct a narrow beam of electrons to selected locations on the target to change the electrical potential of the affected surface in those locations. One or more flood guns are provided to direct a wide, unfocused beam, or cloud, of electrons onto the target to restore the potential of the affected surface to the potential of the flood gun cathode. A collector is placed next to the target circumference to collect secondary electrons emitted by and electrons from the flood gun reflected from the target, maintaining the collector potential at a value just below it. first transition point of the target secondary emission characteristic so that the target can be written and recovered at high speed by the writing gun. The writing gun, flood gun and collector are placed outside a predetermined field of view of the liquid crystal cell window so that light can be transmitted through the cell to the target for modulation.

A projection system is composed by providing a cathode ray tube with a writing gun, a flood gun, a collector, and the liquid crystal cell, the liquid crystal cell set plate forming the cathode ray tube set plate. An access window is formed on the back of the cathode ray tube so that light can be transmitted into the access window and directed through the liquid crystal cell. Polarizing material is placed in front of the access window and in front of the adjusting plate so that the liquid crystal cell 15 can be used to modulate the intensity of the light by varying the polarization of light passing through it. A lens system is arranged to direct light from a light source through the cathode ray tube and project the outflowing light.

The light valve is constructed according to a method that results in an isostatic liquid crystal cell. The adjusting plate is made by depositing an indium tin oxide coating on one surface to form the transparent electrode and providing a supply and an outlet through the adjusting plate, the outlet of which is connected to a collection chamber. The target is placed on the set plate and mounted on its periphery, the target separated from the electrode by a peripheral spacer. The space within and around the cell is evacuated, after which thoroughly degassed liquid crystal material 30 is forced through the feed under pressure until the cell is completely filled, after which the feed is closed. Then the pressure on the outside of the target is increased until the target is nearly parallel to the set plate, after which the drain is closed. It has been found that nematic liquid crystal material with high birefringence, low dielectric anistropy, low viscosity at room temperature is particularly suitable.

The object of the invention is therefore to provide in the first plate a new and improved light valve with a liquid crystal to be directed by an electron beam and a method for the manufacture thereof.

The invention further relates to such a light valve in which light is modulated as it passes through the valve.

In addition, the present invention aims to provide such a light valve that is suitable for use in an application with a high writing and recovery speed.

In addition, the invention aims to provide an image projection system 10 in which the above-mentioned light valve is used.

Finally, the object of the invention is to provide a method for assembling the above-mentioned light valve which leads to an isostatic liquid crystal cell.

The above and other objects, features and advantages of the invention will become more apparent from the following description of the invention, with reference to the drawing, in which Fig. 1 shows a schematic side view of a light valve according to the The present invention., FIG. 2 is a graph of the secondary emission characteristic of an example of an electron beam target used in the light valve shown in FIG. 1, showing the relationship of the writing gun and collector potentials with respect to secondary emission, FIG. 3. the shapes of the waves of the current from the writing gun and the electric potential formed on a described region of the above-mentioned target, FIG. 4 is a schematic side view of the light valve shown in FIG. 1, in a projection system according to the invention, Fig. 5 shows a schematic side view of the construction of a light valve according to the present invention.

As shown in Figure 1, the electron beam directed liquid crystal light valve comprises a liquid crystal cell 10, having a front face 12 and a back face 14, a writing electron gun 16 for directing an electron beam at selected locations on the back face of the cell to change the electrical potential at those selected locations, one or more flood electron guns 18 for directing a wide, unfocused beam of electrons on and over the rear face of the cell, and a collector electrode 20 disposed next to the periphery of the back face of the cell to collect the 5 secondary electrons emitted from the back face of the cell and electrons reflected from the back face of the cell. The writing gun, flood gun, and collector electrodes, which must be located at least partially within a substantially evacuated space together with the rear plane of the liquid crystal cell, are arranged in successive locations outside a predetermined field of view of a window defined by the liquid cell As shown by lines 22, this allows light to pass freely through the liquid crystal cell and to be modulated thereby, normally enters the cell window from the rear face 14 and exits through the front face 12.

The liquid crystal cell itself has a setting plate 24 of transparent material, preferably, but not necessarily glass, one side of the setting plate comprising the front face 12 of the liquid crystal cell. A transparent adjustment plate electrode 26 is formed on the other rear face 28 of the adjustment plate. The transparent electrode is suitably a thin film of indium tin oxide (ITO) deposited on surface 28 in a known manner. A target 30 of transparent dielectric material is placed parallel to the set plate at a predetermined distance D from the transparent electrode 26 defined by a spacer 32, wherein the back face, or outside face, of the target is the back face 14 of the liquid crystal cell. A layer of a nematic liquid crystal material 34 fills the space between the transparent set plate electrode 26 and the target 30. A seal 35 of an epoxy compound or other suitable material extending around the periphery of the cell prevents the liquid from flowing. crystal material escapes. The surfaces of the electrode 26 and target 30, which are in contact with the liquid crystal layer, are suitably treated to provide a parallel (homogeneous) boundary orientation, with the orientations of the two surfaces 83 03 55 1 -8 right angles shapes to provide a 90 ° twist in the nematic liquid crystal material. Such a surface orientation is preferably obtained in a known manner by depositing a transparent film of silicon monoxide (SIO) in vacuum on the surfaces at an angle of about 5 ° to the surface.

It has been found that float glass is a suitable material for the adjustment plate, and that a tensioned, transparent dielectric membrane of a material such as mica, polyimide or glass is suitable for the target, although other materials can be used satisfactorily. The target 30 material, after being treated or not, must have a secondary electron emission ratio (δ) that is greater, and preferably significantly greater, than 1 when it is hit by electrons from a writing electron gun. Spacer 32 suitably consists of a polyester film (such as that sold under the designation Mylar, a trademark of E.I. du Pont de Nemours & Co.) or fritted glass.

In the joined cell, the molecules of the nematic liquid crystal material 34 are arranged such that planar polarized light passing through the cell rotates 90 ° in the absence of an applied electric field. When a voltage is applied across a region of the material, the molecular axes of the liquid crystal molecules in that region attempt to align parallel to the applied field, thereby decreasing the angle of rotation of the polarized light through that region of the cell. The liquid crystal material therefore modulates the light by shifting its polarization. When sufficient voltage is applied, the polarized light passes unchanged through the "altered" region of the cell.

Commercially available nematic liquid crystal materials suitable for use in cell 10 include 35 E. Merck's Nematic Phase 1132TNC, a mixture of three individual phenylcyclohexanes and a biphenylcyclohexane, and BDH Chemical's E7, a 4-cyan eutectic mixture 4'-n-penta-biphenyl, 4-cyano-4 "-n-pentyl-p-terphenyl, 4-cyano-4'-n-heptylbi-phenyl and 4-cyano-4'-n-octoxybiphenyl. ideally, the nematic liquid crystal material has high birefringence (eg Δη> 0.15), low dielectric anisotropy and low viscosity at room temperature Materials with such properties are preferable because they have the writing beam current 5 is required to switch the cell at speeds suitable for standard monochromatic television image presenters to minimize Liquid crystal compositions with such combination of physical and electrical properties are the subject of the present invention. The co-pending patent application entitled, "Translucent Liquid Crystal Materials for Use in Electro-Optical Presentation Devices". However, as an example, a preferred nematic material exists with ^ a Δη> 0.16, a £ 11 <13, and £ 1 <6, and a viscosity4. 40 cp 15 at 20 ° C, mainly from a mixture containing 80 wt% of an eutectic from BDH Chemical's K15 and E. Merck's S1103, and 20 wt% of E. Merck's S1544.

The writing electron gun 16 can be formed in a number of ways suitable for a cathode ray tube, as is well known in the industry of presentation technology. Likewise, flood guns 18 can be formed in a number of ways, as is well known in the presentation technology industry for the manufacture of storage type cathode ray tube display devices.

The shape of the collector of the light valve is particularly important since it is necessary that an electrode be present to receive secondary emission electrons from and flood gun electrons reflected from the back face 14 of the dielectric target 30, while simultaneously light obstructed is transmitted through the liquid crystal cell 10, and an electric potential image is written on the back face 14 of the target. It is preferable that the collector be formed from a conductive ring 20 placed around the periphery of the liquid crystal cell, the central axis protruding from the adjustment plate 24, as shown in Fig. 1, the target 30 of the cell being circular is. The collector electrode is then outside the field of view of the cell window, represented by lines 22, with a fairly uniform electric field connected to the collector around the periphery of the cell.

In operation, the rear face 14 of the target 30 is usually held at the same potential V ^g as the cathode of the flood gun 18, because the flood gun continuously has an electron cloud on and over the back face that has the same potential V as the flood gun. Flood gun electrons fg bounce back, while regions of the rear face which are positive to flood gun electrons attract until such regions acquire a potential, with additional 10 free electrons being attracted by the collector 20. The target 30 acts as a capacitor, as does liquid crystal material 24; the voltage across a certain region of the liquid crystal material, and therefore the polarization switching effect, is therefore a function of Vg, the potential 15 Vg of the transparent plate electrode 26, and the capacitance of the target with respect to the target. capacity of the liquid crystal material in that region. The flood gun cathode is typically electrically connected to the transparent electrode so that the transparent electrode and the backplane of the target usually have the same potential, keeping the liquid crystal material in an unconverted state with no bias. In some circumstances, however, it may be desirable to bias the cell, in which case the flood gun cathode and electrode 26 should not be connected together.

The write gun cathode 16 is operated with a very high negative potential V ^ g relative to the flood gun cathode potential V ^ g, in particular about 4.5 kV, so that when the write beam strikes the back face 14 of the target plate more electrons are emitted than are absorbed, as shown by the secondary emission curve of Fig. 2. The region of the target hit by the electrons of the writing gun acquires a positive potential which is capacitively coupled to a corresponding layer of the liquid crystal, whereby that area is switched.

Since the target material is dielectric, a collector must be present in the vicinity to provide a return path for the writing and flood guns. To perform this function, the collector must necessarily direct the target. Areas of the rear face '8 3 0 3 5 5 1 -11- have a positive potential with respect to both the write and flood gun cathodes, although, in order to be able to restore the flood guns to areas affected by the write gun beam, instead of stabilizing at the collector potential VcQ ^, the collector potential should be lower than the target's first alternating potential Vcr ^, i.e. the lowest potential corresponding to the electron energy at which the secondary emission ratio δ is equal to one. This allows the light valve to be used in a quick display writing and recovery device, rather than as a storage device.

As shown in FIG. 3, when an area of the rear face 14 of the target is hit by the write gun beam, the potential in that area increases to, but not higher than, the collector potential VCQ. Since the collector potential is less than Vcr1, more flood gun electrons are then absorbed than emitted, so that the potential in that region drops until after the current of the writing gun has stopped in that region. In this manner, a potential image on the target can be written by the writing gun, then erased by the flood gun, and then rewritten by the writing gun.

This image is capacitively coupled to the liquid crystal, which modulates the light passing through it according to the image.

It has been found that by using the above-mentioned preferred nematic liquid crystal material disposed in a cell with a separation distance D of 10 M, an image can be obtained which is for projection of a mono-chromatic television image at a wavelength of 0.6 x 10 ~ ^ M is satisfactory. Using a writing gun that has a beam current of 14.7 x 10-6 amps. and providing a beam width of 4.4 mil, and a stressed micro target, the following results can be obtained: 35 presentation switching speed 25 msec contrast ratio 59: 1 resolution 225 lines per inch writing speed 164 cm / msec

As shown in Fig. 4, a projection device employing a light valve of the present invention also includes an evacuated chamber 36 containing the writing gun 16, flood guns 18, and a collector electrode 20, the liquid crystal cell 10 being attached to the front of the chamber with the rear face 14 facing inward. Preferably, an access window 38, which includes an opening covered with a transparent material, is disposed on the back of the chamber 36 and the writing gun 16 is positioned off-axis so that an unobstructed field of view through the access window 38 and the window defined by the liquid crystal cell 10 is present. A first polarizer 40 is placed behind the access window to polarize light flowing in through the access window and a second polarizer, or analyzer 42, is placed in front of the cell 10 to cause only light of a selected polarity to flow through it without reduction in intensity . The polarizer 40 and the analyzer 42 may be made of commercially available polarizing sheet materials.

The intensity of the light flowing through the analyzer from a certain area of the liquid crystal cell will depend on the extent to which that area is MinM switched by the writing gun, because the intensity of the light flowing through the analyzer depends on the relative polarization of the analyzer and the light incident on it.

The polarization modulation formed by the switched nematic liquid crystal cell is therefore converted by the polarizer and analyzer into intensity modulation. When the polarization of the analyzer has the same direction as the polarizer 30, the intensity of the acquired image will increase with the intensity of the electron beam of the writing gun, while when the polarization of the analyzer is rotated 90 ° relative to the polarization of the polarizer the intensity of the image will decrease with increasing intensity of the electron beam of the writing gun.

A lens 44 is provided to direct light from a source, such as a lamp 46, through the access window 38 and through the window of the liquid crystal cell 10. Another lens 48 is provided to image the liquid crystal cell, 3303551 - 13- to focus on an image surface, such as the surface of screen 50, projecting on the screen the image represented by an electric supply signal to the writing gun. While a simple optical system represented by lenses 44 and 48 is shown here, it will be appreciated that more complicated optical devices may be employed depending on the particular application in which the light valve is used.

It has been found that a suitable light valve can be assembled as shown in Figure 5. A float glass target 52, or any other suitable transparent material, is made by first coating a layer of indium tin oxide (ITO) on known surfaces. way, to form a transparent electrode 54, and then a thin, transparent, aligned film of silicon monoxide (not shown) on the surface of the ITO electrode 54. The aligned film can be deposited by vacuum-depositing silicon monoxide at an angle of 5 ° from the plate surface according to a method such as that described by J. Janning in Appl. Phys. Lett., Vol. 21, p. 173 (1972). A supply opening 56 and a discharge opening 58 are formed in the adjusting plate, and supply and discharge tubes 60 and 62 are sealingly mounted on the adjusting plate, and connected to the respective openings. A glass vacuum ampoule, or chamber 64, is sealingly connected to the remaining end of the drain tube. In this arrangement, the set plate is placed horizontally and then a target 66 above the translucent indium tin oxide electrode 54, which rests on a peripheral spacer 68 and is circumferentially mounted on the coated set plate by a closure 70 using an epoxy compound or other suitable sealant. The target 66 contains λ a transparent, aligned silicon film on its inner surface, which is rotated 90 ° relative to the aligned film on electrode 54.

Thereafter, the space between the target 66 and the transparent electrode 54 is filled with the liquid crystal material. This takes place by first evacuating the space directly around and in the adjusting plate, target, supply tube, discharge tube and ampoule. Then, the free end of the feed tube 60 83 0 3 5 5 t ♦ -14- is introduced into the thoroughly degassed liquid crystal material and the pressure on the liquid crystal material is increased, resulting in it flowing into the cell via the feed tube 60, the fills the space between the adjusting plate 52 and target 66, and flows out of the discharge tube 62 and into the ampoule 64. After the space between the adjusting plate and target is completely filled, the supply tube 60 is clamped at a suitable point 72 by known means and the press the external surface of the target 66 enlarged until the target rests firmly on the circumferential spacer 68 and is substantially parallel to the adjustment plate. Then, the discharge tube 62 is clamped at a suitable point 74 to trap the liquid crystal material in the cell. By performing the above-mentioned method, using a thoroughly degassed liquid crystal material, an isostatic liquid crystal cell is formed, ensuring uniform plate separation and high vacuum structural stability.

A suitable clamping clamp 76 for pressing liquid crystal material into the cell is shown in Fig. 5. The feed tube 60 is sealed to an upper portion 77 of the clamping clamp through a cap with screw thread 78, washer 80 and resilient 0-. ring 82, the feed tube extending down through an upper chamber 84 and lower chamber 86 of the upper portion of the chuck.

When vacuum has been applied in the cell and the surrounding space, a lower portion 88 of the chuck containing a liquid crystal container 92 is screwed up into the lower chamber 86 of the upper part of the screw thread until it covers the openings 94, which are provided to evacuate the interior of the chuck, and is fitted against a plug 96, an O-ring is provided to obtain a pressure lock, the feed tube being introduced into the liquid crystal material brought.

The pressure on the liquid crystal material 92 is increased to force it into the feed tube 60 by feeding a gas into the upper chamber 84 through a feed opening 100. Preferably, such a gas should be inert and have a low solubility in the liquid crystal material, and argon has proved to be the most suitable, although other gases 53 03 55: -15- can be used without exceeding the scope of the invention.

The first evacuation of the cell and the surrounding space can take place by placing the whole in a bubble vessel and evacuating the bubble vessel. When the cell is completely filled with the liquid crystal material, the pressure in the bubble vessel is increased to increase the pressure on the external surface of the target 66, as discussed above.

When the liquid crystal cell is built up, it can be mounted on, or incorporated into, a suitable structure with a writing gun, a flood gun and a collector electrode and used to place the valve in a vacuum, such as a cathode ray tube, to serve.

On the other hand, when the cell is used as a cathode ray tube adjusting plate 15, it is attached to the funnel 102 of the cathode ray tube before it is placed in the bubble vessel. In that case, the pressure on the outside of the target 66 is increased by increasing the pressure in the cathode ray tube, preferably with an inert gas such as argon.

The cathode ray tube is heated in a known manner to remove gases, in particular water vapor, before it is closed. The cell is attached to the funnel 102 with an epoxy compound although other known fasteners may be used, and this epoxy compound, as well as other compounds used in the valve assembly, is selected in this case from commercially available epoxy compounds which can withstand the high temperature of about 300 ° C necessary for the heat treatment of the cathode ray tube for a short time.

3Q The switched, nematic, liquid crystal cell used in the light valve of the present invention is not limited to the cell type described above. Other switched nematic cells that can be used include flow sensitive cells of the type described by R. Hubbard and D. Bos in "Optical-Bounce Removal and Turnoff-Time Reduction in Twisted-Nematic Displays". IEEE Trans.Elec. Dev., Vol. ED-28, No. 6 biz. 723 (1981). Also useful are dual frequency directional nematic cells made using liquid crystal materials of the type described in a publication by R. Hubbard et al., Entitled, "Development of Dual-Frequency Addressable Liquid Crystals". , presented at the fourth annual symposium on Liquid Crystals and 5 Ordered Fluids on April 1, 1982 in Las Vegas, Nevada.

0 t 83C3S5 1

Claims (9)

An electron beam-directed liquid crystal light valve for modulating transmitted light in an image projection system, characterized in that the system comprises: 5 (a) a liquid crystal cell with a transparent mounting plate comprising a transparent electrode mounted on one surface thereof, a transparent target disposed on the same side of the adjusting plate as the transparent electrode and substantially parallel to and at a predetermined distance from the transparent electrode, the target having a target surface on its side opposite the transparent electrode, liquid crystal material is disposed between the target and the transparent electrode, and sealing means for retaining the liquid crystal material between the target and the transparent electrode, a portion of the cell being defined by the adjustment plate, transparent electrode and target, b) writing gun means for modifying the electric potential at selected locations on the target surface by directing an electron beam onto this target surface, (c) flood gun means for restoring the electric potential on the target surface to a predetermined value by directing an electron cloud at the target surface, and 25 ( d) collecting means disposed adjacent to the periphery of the target for collecting electrons emitted and reflected from the affected surface, the flood gun means, writing gun means and collecting means disposed outside a predetermined field of view through the cell window. 2. Light valve according to claim 1, characterized in that the liquid crystal material is a natural type material. 3. Light valve according to claim 2, characterized in that the nematic liquid crystal material has a high birefringence, low dielectric anisotropy, a low viscosity at room temperature. 4. Light valve according to claim 1, characterized in that the liquid crystal material modifies the polarization of the transmitted light by an electric field applied thereto, and also comprises polarizing means for polarizing light before it passes through the cell window and analyzer means for receiving light that has passed through the window and transmitting this light at an intensity that depends on the polarization of the received light. Light valve according to claim 4, characterized in that there are also optical system means for receiving light from a light source, which direct the light through the polarizing means, then through the cell window, and finally through the analyzer means, and light to be projected through the analyzer means. 6. Light valve as claimed in claim 1, characterized in that also a first aligned film applied to the transparent electrode and a second aligned film applied to the target are present, wherein both films are in contact with the liquid crystal material, to arrange the liquid crystal material, while the first and second aligned films have a predetermined orientation relative to each other. 7. Light valve according to claim 1, characterized in that there is furthermore a substantially evacuated chamber mounted on the liquid crystal cell, wherein the target surface of the target faces the interior of the chamber, flood gun means and write gun means emit electrons in the chamber, the collector means having an electron collecting electrode disposed in the chamber adjacent the periphery of the cell, and the chamber having an access window for receiving light from the chamber and transmitting the light to the target surface. Light valve according to claim 1, characterized in that means are also present, connected to the collector means and the flood gun means for forming a positive potential on the collector means with respect to the flood gun means wherein the potential is smaller than the first alternating potential of the target secondary electron emission curve. Light valve according to claim 1, characterized in that the target contains a tensioned dielectric membrane. i 83 0 3 5 5 f